Can controlled-release urea replace the split application of normal urea in China? A meta-analysis based on crop grain yield and nitrogen use efficiency

Normal urea (NU) often requires multiple applications to increase crop yield and nitrogen (N) fertilizer utilization efficiency by improving the synchronization of crop N demand, which increases the labor input. Controlled-release urea (CRU) has excellent N release performance, and it can significantly increase crop productivity with only one application as a base fertilizer. However, there is still a lack of comprehensive evaluation of whether CRU can replace the split application of NU (split-NU) to increase crop yield and N fertilizer use efficiency, as this would reduce the necessary labor. Therefore, the aim of this study was to evaluate whether CRU can replace split-NU nationwide. To this end, we collected peer-reviewed articles on CRU and split-NU that were published in recent decades and performed a meta-analysis. The results showed that, compared with all NU as base fertilizer, CRU and split-NU increased crop yield by 10.08% and 8.11%, respectively, and N use efficiency by 47.55% and 45.21%, respectively. In general, CRU had a better substitution effect on split-NU nationwide. However, due to regional climate factors, soil physicochemical factors, and field management measures, the substitution effect of CRU on split-NU varied. In most cases, CRU had a good substitution effect on split-NU, but when the soil available N content (< 50 mg kg- 1) and the N application rate (< 150 kg ha- 1) are both low, the planted crop was wheat, CRU had a poor substitution effect on split-NU. In addition, we found that CRU had a good substitution effect on split-NU in reducing N loss (greenhouse gas emissions and nitrate leaching) and increasing economic benefits. Therefore, we highlighted the threefold benefits of CRU, as it can improve crop productivity, reduce N loss, and decrease labor input; thus, it can be widely applied nationwide.